Field Testing the New Open-Path and Enclosed-Path CO2/H2 O Flux Measurement Systems.

In 2014-2015, new open-path and enclosed-path flux measurement systems were developed with an ultimate goal of reducing errors in CO₂ and H₂O hourly fluxes and in long-term carbon and water budgets.  

The new systems are based on established LI-7500A and LI-7200 gas analyzer models, with the focus on improving stability in the presence of contamination, refining temperature control and compensation, and providing more accurate gas concentration measurements.

In addition to optical and electronic redesign, both new systems incorporate automated on-site flux calculations using EddyPro® software run by a weatherized remotely-accessible microcomputer, SmartFlux 2.

Field tests of both systems were conducted over six periods, each 5-14 months long, at 6 sites with diverse environments, setups, and types of contamination, using 26 gas analyzers.

The open-path LI-7500RS system performed significantly better than the original LI-7500A model in terms of contamination-related drifts in mean concentrations. Improvements in CO₂ drifts were strong, with RS models often drifting few-to-tens of times less than the original. Improvements in H₂O contamination-related drifts were particularly significant, with modified models often drifting many tens of times less than the original.

The enclosed LI-7200RS system performed substantially better than the original LI-7200 in terms of the drifts in H₂O, sometimes drifting few-to-tens of times less than the original. Improvements in CO₂ contamination-related drifts were modest, being similar or just a bit better than the original.

Results from field tests suggest that both new RS systems can help improve data quality, flux data coverage and potentially reduce site maintenance.

The presentation will describe details and latest results from field tests of these new models in comparison with older models and control reference instruments.